How does a radio filter out waves of different frequencies?
How does a radio filter out waves of different frequencies?
With all the different frequencies of waves in the air, how does the sound out of a radio come out clear?What do I need to make one?
dear radio does not filter any waves!! let me explain..
Radio has a demodulator in it. it is a PLL. now the demodulator ics like MM74HC4046 are connected in a standard circuit. when you tune the radio for a frequency, which is actually changing the resistor values for the oscillator, you demodulate the frequencies one by one. supose your range is from 300 KHz to 10 MHZ then as you turn the knob, and your circuit has range 300KHz – 12 MHZ thn your starting freq is 300KHz. then as you turn the knob you increase or decrease the resistance and start tuning the circuit. then your first station is at 598khz. at that freq u hear the channel. then as you turn along it goes higher. at 3.9MHZ you listen to different channel. so thats no problem. also the PLL is there which gets locked at a frequency and so there is a conitnuous demodulation at this frequency. I’ve already told you one ic and there are many others. also another is 7046.
if you want ot make one then search FM demodulators by 4046 and use the MM74HC4046. it gives higher selection from short wave, medium wave and FM also.
March 26th, 2010 at 1:14 pm
dear radio does not filter any waves!! let me explain..
Radio has a demodulator in it. it is a PLL. now the demodulator ics like MM74HC4046 are connected in a standard circuit. when you tune the radio for a frequency, which is actually changing the resistor values for the oscillator, you demodulate the frequencies one by one. supose your range is from 300 KHz to 10 MHZ then as you turn the knob, and your circuit has range 300KHz – 12 MHZ thn your starting freq is 300KHz. then as you turn the knob you increase or decrease the resistance and start tuning the circuit. then your first station is at 598khz. at that freq u hear the channel. then as you turn along it goes higher. at 3.9MHZ you listen to different channel. so thats no problem. also the PLL is there which gets locked at a frequency and so there is a conitnuous demodulation at this frequency. I’ve already told you one ic and there are many others. also another is 7046.
if you want ot make one then search FM demodulators by 4046 and use the MM74HC4046. it gives higher selection from short wave, medium wave and FM also.
References :
March 26th, 2010 at 2:00 pm
A variable capacitor and an inductor are arranged as a filter circuit that passes only one frequency, and cancels out the rest.
When you turn the know on the radio, you cause moving metal plates to move past each other, which changes the value of the variable capacitor.
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…The simplest tuner consists of an inductor and capacitor connected in parallel. The capacitor is usually made to be variable (although the inductor can made variable it requires a more complex mechanism and is rarely used). This creates a resonant circuit which responds to an alternating current of one frequency. In general, radio makers will use a rule of thumb of 1.5 picofarads per metre wavelength. Common inductance values are 4.1 milliHenries for long wave, 370 microHenries for medium, and 130 nanoHenries for VHF (FM) between 88 and 108 MHz. In a superheterodyne radio the capacitor that tunes the "tank" will be ganged with another; this alters the local oscillator to provide a constant intermediate frequency. Combined with a detector, also known as a demodulator, it becomes the simplest radio receiver, often called a crystal set…
References :
http://en.wikipedia.org/wiki/Tuner_(radio)
http://www.radio-electronics.com/info/circuits/lc_bandpassfilter/lc_bpf.php
http://en.wikipedia.org/wiki/Demodulation
March 26th, 2010 at 2:34 pm
There are four kinds of RF (radio frequency) filters; low pass, high pass, band pass and notch. Low pass filters allow signals below a specific frequency to pass. High pass, signals above the specific frequency can pass. Band pass filters allow signals between two frequencies to pass, kind of like a high pass and low pass filter back to back. A notch filter is an inverse of band pass filter, a narrow range of frequencies are rejected while the rest go through.
This is accomplished by using various combinations of coils and capacitors (or by integrated circuits). There are two types of electrical AC resistance; inductive reactance and capacitive reactance. RF is a form of AC and thus, is effected by reactance. Both kinds of reactance vary with frequency and are inversely related to each other. Inductive reactance is a property of coils. Capacitive reactance is a property of capacitors. There will be a frequency where capacitive reactance and inductive reactance cancel out. This frequency is determined by the value of the coil and capacitor used. This cancellation creates a high or low impedance depending on the circuit configuration. Impedance is the total resistance to current flow which includes reactance and regular resistance. When the impedance is high, the signal is blocked. When the impedance is low, the signal passes.
Sounds like you are interested in making a radio receiver. There are very simple ways to do this like in the link below. More sophisticated radios take a little more knowledge. There are radio receiver kits out there you can build. I built one when I was 10. You might be interested in Amateur Radio. Hams are all about building radio equipment . This includes receivers and transmitters. You can build this stuff and then use it to talk to other Hams around the world.
References :
http://www.youtube.com/watch?v=skKmwT0EccE